"The productive factors enter into the production of different commodities in very different proportions."

“I started to write on the foundations of an approach to international trade theory that was to some extent new and for which I received the inspiration during a stroll on Unter den Linden in Berlin in 1920.”

“To me it is a riddle that, who for most of his life was a fanatical representative of extreme opinions in the social debate, could present a completely different personality in the scholarly context. During the period when I knew him he was the diffident seeker after scientific truth.”

“International trade theory has, in my opinion, given far too much attention to the effects of certain variations, for example, in duties, on the national incomes, and too little to the effects on individual incomes. In many cases, changes in the sums count for very little, while changes in the individual incomes are distinctly relevant.”

“Curiously enough, John Stuart Mill, although he must have been familiar with Longfield's writings, seems never to have touched upon this line of reasoning.”

“I am presently at work on a dissertation dealing with the theory of international trade and foreign exchange rates. In dealing with this, studies of the intervention of recent years in the area of trade and exchange rates of different countries is of the greatest importance. I therefore hope to be able to begin a six month study tour to Switzerland, France and England at the end of May this year. After having collected the necessary material I intend — if the economic side can be arranged — during a stay of 6–12 months in England or possibly the United States — to work out the above mentioned dissertation as a specimen for the doctoral degree in philosophy and pursue studies in general. I have not yet any detailed study plan. That should appropriately be set up after the arrival.”

“The origin of this research was an attempt to extend Cassel’s system of equations of price determination in one market to that of several trading countries. Although the point of departure is totally different, the results of that attempt exhibit important similarities to Heckscher’s treatment in ‘‘The Effect of Foreign Trade on the Distribution of Income,’’ published one year earlier in Ekonomisk Tidskrift, 1920. There is no doubt that the author was unconsciously influenced by Heckscher’s paper both at this and at later stages of the work. The influence of this pathbreaking paper, both conscious and unconscious, has surely been particularly decisive in the development of the material in chapters I–III.”